Execution Time of VHDL code

VHDL is not like a programming language.

The operations it describes are generally not sequential but parallel, since they are implemented in a PLD as combinatiorial logic, physical registers and so on.

These logic elements continuously 'execute' their function at any time: there's not a 'program counter' which activates them sequentially.

Rather than execution time, we speak of timing, and this involved the propagation path of signals between the logic elements of the design.